i'm afraid this is going to be a wall of text, but i'll try to be as detailed as i can in describing this problem that has my mechanic and i totally stumped. the car is an 88 n/a 5sp.
noticing how poorly the car ran (really low on power, really bad on fuel economy), we first thought it was a fuel issue. all of the ignition components are new, so a fuel problem was our best bet. though we didn't actually get into changing the fuel pump and filter, we have reason to think there's another problem instead.
we were thinking that it may be a classic BHG almost a month ago-the car overheated on me, the coolant was way low, and the radiator/coolant system would be highly pressurized after running the car for even a few seconds. coupled with the poor performance, it seemed to fit. however, the overheating was explained away due to a stuck thermostat and the pressurized coolant system and missing coolant was explained away to a bad radiator. both of those problems were fixed.
before changing the fuel filter and pump, my mechanic thought to check the timing, as it may have been slightly off and throwing the system off. as it turns out, there is something really screwed up! if the car is perfectly in-time, it will start up and idle (like a champ) but that is it. it won't respond at all to any throttle input and will only idle, sounding pretty but not moving. the only way the car will move under its own power is if both cams are one tooth retarded and the ignition is one tooth retarded and the distributor is turned all the way advanced. what's more, the idle speed is constantly at 1200 rpms. after playing around with the timing and then setting it back OUT of time like it initially was in order to drive back home and troubleshoot, the idle dropped to around 750, but loped and missed terribly. after driving for a while, it seems to have returned to a more solid feel at 1200 rpms.
we've checked the cams, the timing gears, the CPS, everything that could be installed incorrectly to give a false impression of a car's timing, but it's all ok. we pulled codes on the computer and got only code 51-either ECU or TPS. i'm buying a new TPS, as it was cheaper than the ECU to try first, but if that doesn't solve the problem, and if the ECU doesn't solve the problem, then we are out of ideas. i'm sure there are a few more things we've tried, but i can't quite remember at the moment.
points of interest/question are if a BHG is still on the table and if one or more of the ignition components may be wrong.
the BHG is still questionable because i seem to still be inexplicably losing coolant (the radiator is full but the overflow tank was empty yesterday evening), i am losing oil without any leaks (but could simply be an old engine burning it off), and though it hasn't overheated since that one time when the thermostat was stuck, it typically runs at a temp slightly higher than half. we did a coolant system compression test this morning-the system wouldn't hold and lost 3 psi. as i was given to understand, a BHG would see that coolant pushed into one of the cylinders when the engine is off and the coolant system is pressurized, making it hard to start and making the engine misfire for a few seconds. however, the car started immediately and didn't miss. the exhaust has no coolant/oil smell at all and doesn't smoke. so a BHG is maybe still possible, but also maybe not very likely.
the other point of interest/question is concerning one or more of the ignition components. all of them were new when i got the car a few months ago, so i didn't get to oversee the accuracy of the ordering. i'm wondering if the previous owner ordered a distributor for a turbo supra, either by mistake or thinking that it would boost performance. the turbo distributor would drop right in and install, but may also give all kinds of problems like we're seeing.
i'm sure there are more clues and/or pieces to the puzzle, but i can't quite think of them at the moment. please please, if you have any ideas, throw them here. if it's something we've tried, it will remind me and we can continue the differential diagnosis, but we are so out of ideas. thanks so much for the help, anyone who can.
noticing how poorly the car ran (really low on power, really bad on fuel economy), we first thought it was a fuel issue. all of the ignition components are new, so a fuel problem was our best bet. though we didn't actually get into changing the fuel pump and filter, we have reason to think there's another problem instead.
we were thinking that it may be a classic BHG almost a month ago-the car overheated on me, the coolant was way low, and the radiator/coolant system would be highly pressurized after running the car for even a few seconds. coupled with the poor performance, it seemed to fit. however, the overheating was explained away due to a stuck thermostat and the pressurized coolant system and missing coolant was explained away to a bad radiator. both of those problems were fixed.
before changing the fuel filter and pump, my mechanic thought to check the timing, as it may have been slightly off and throwing the system off. as it turns out, there is something really screwed up! if the car is perfectly in-time, it will start up and idle (like a champ) but that is it. it won't respond at all to any throttle input and will only idle, sounding pretty but not moving. the only way the car will move under its own power is if both cams are one tooth retarded and the ignition is one tooth retarded and the distributor is turned all the way advanced. what's more, the idle speed is constantly at 1200 rpms. after playing around with the timing and then setting it back OUT of time like it initially was in order to drive back home and troubleshoot, the idle dropped to around 750, but loped and missed terribly. after driving for a while, it seems to have returned to a more solid feel at 1200 rpms.
we've checked the cams, the timing gears, the CPS, everything that could be installed incorrectly to give a false impression of a car's timing, but it's all ok. we pulled codes on the computer and got only code 51-either ECU or TPS. i'm buying a new TPS, as it was cheaper than the ECU to try first, but if that doesn't solve the problem, and if the ECU doesn't solve the problem, then we are out of ideas. i'm sure there are a few more things we've tried, but i can't quite remember at the moment.
points of interest/question are if a BHG is still on the table and if one or more of the ignition components may be wrong.
the BHG is still questionable because i seem to still be inexplicably losing coolant (the radiator is full but the overflow tank was empty yesterday evening), i am losing oil without any leaks (but could simply be an old engine burning it off), and though it hasn't overheated since that one time when the thermostat was stuck, it typically runs at a temp slightly higher than half. we did a coolant system compression test this morning-the system wouldn't hold and lost 3 psi. as i was given to understand, a BHG would see that coolant pushed into one of the cylinders when the engine is off and the coolant system is pressurized, making it hard to start and making the engine misfire for a few seconds. however, the car started immediately and didn't miss. the exhaust has no coolant/oil smell at all and doesn't smoke. so a BHG is maybe still possible, but also maybe not very likely.
the other point of interest/question is concerning one or more of the ignition components. all of them were new when i got the car a few months ago, so i didn't get to oversee the accuracy of the ordering. i'm wondering if the previous owner ordered a distributor for a turbo supra, either by mistake or thinking that it would boost performance. the turbo distributor would drop right in and install, but may also give all kinds of problems like we're seeing.
i'm sure there are more clues and/or pieces to the puzzle, but i can't quite think of them at the moment. please please, if you have any ideas, throw them here. if it's something we've tried, it will remind me and we can continue the differential diagnosis, but we are so out of ideas. thanks so much for the help, anyone who can.
